1. Field of the Invention
The present invention relates to the preparation of diorganopolysiloxanes having alkoxy endgroups, hereinafter designated FP (functionalized polymers). This invention also relates to the use of such alkoxylated diorganopolysiloxanes as one of the essential constituents of single-component organopolysiloxane elastomer compositions which are stable in storage, in the absence of moisture, and which are cross-linked by atmospheric moisture at ambient temperature, namely, cold-vulcanizable elastomer compositions (CVE).
2. Description of the Prior Art
It is known to this art to prepare such FPs by reacting a di- or tri- or a tetraalkoxy silane with a diorganopolysiloxane oil containing a hydroxyl group bonded to the silicon atom at each end of its polymer chain, but it is necessary to employ a catalyst therefor. Many patents claim the use of specific catalysts for this functionalization reaction.
U.S. Pat. No. 3,542,901 describes an amine as a catalyst. This catalyst is effective, but the reaction is fairly slow (for example 15 to 30 min at 60.degree. C. in the case of fairly reactive alkoxysilanes such as Si(OCH.sub.3).sub.4 or ViSi(OCH.sub.3).sub.3). With relatively unreactive alkoxysilanes, it is necessary to employ much longer times or else to obtain only incomplete reactions. It is also known to this art that the presence of residual silanols is generally detrimental to stability (see U.S. Pat. No. 4,489,191 and French Patent Applications Nos. 2,597,876 and 2,597,877). In addition, it is difficult to remove the amine completely, and this may have a detrimental effect on the storage stability of the composition; it can also cause the appearance of yellowish discolorations either during the storage of the compound or on the crosslinked product.
Thus, many other catalyst systems have been proposed for such purpose, including:
Potassium acetate: U.S. Pat. No. 3,504,051; PA1 Various inorganic oxides: FR 1,495,011; PA1 Organic titanium derivatives: U.S. Pat. No. 4,111,890; PA1 Titanate plus amine: U.S. Pat. No. 3,647,846; PA1 Alkoxyaluminum chelate: GB-A-2,144,758; PA1 N,N'-Disubstituted hydroxylamine: FR-A-2,508,467; PA1 Carboxylic acid plus amine: FR 2,604,713; PA1 Carbamates: EP 0,210,402; PA1 Organic compounds containing an oxime functional group: FR 2,597,875.
Certain of these catalysts are a little more active than the amines, but it is nevertheless necessary to heat the reaction mass to 60.degree.-70.degree. C. to obtain functionalization times of 5 to 10 minutes. In addition, these catalysts, or their residues, can have a detrimental influence on the storage stability, especially in the presence of curing catalysts, and on the properties of the crosslinked product, because it is difficult or impossible to remove them completely after reaction.
Another process for preparing functionalized oils (FPs) entails the use of mixed silanes which, in addition to the alkoxy groups, contain a hydrolyzable group such as an amido, amino, carbamate, oxime or similar group, optionally in the presence of a known functionalization catalyst and of a polyalkoxy silane.
Processes of this type are described, in particular, in U.S. Pat. Nos. 3,697,568 and 3,896,079, and in EP-A-69,256.
These processes are efficient, but require the use of costly mixed silanes. Furthermore, the organic products originating from the hydrolyzable groups after reaction can have a detrimental effect on the CVE composition (in this regard, compare pages 4 and 5 of French Patent FR-A-2,543,562).